Microlens device and related methods

ABSTRACT

Implementations of semiconductor devices may include: a microlens array formed of a plurality of microlenses. Each of the plurality of microlenses may have a first side and a second side. A layer of polymer may be formed over the second side of each of the plurality of microlenses and a low index box may be between adjacent microlenses of the plurality of microlenses.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of the earlier U.S. Provisional Patent Application to Min Jang entitled “Multi-Layered Microlens Systems and Related Methods,” application Ser. No. 62/955,712, filed Dec. 31, 2019, now pending; this application also claims the benefit of the filing date of the earlier U.S. Provisional Patent Application to Min Jang entitled “Multi-Layered Microlens Systems and Related Methods,” application Ser. No. 62/957,548, filed Jan. 6, 2020, now pending, the disclosures of each of which are hereby incorporated entirely herein by reference.

BACKGROUND 1. Technical Field

Aspects of this document relate generally to microlens devices, used in image sensing devices for automotive, security, or mobile devices. More specific implementations involve global shutter pixel devices.

2. Background

Image sensor devices are used to create an electrical image of incident light using a plurality of pixels. The pixels receive incident light and then generate electron/hole pairs which are then gathered by the device. Digital signal processors are used to process the signals from the pixels to generate an image of what is being observed by the image sensor device.

SUMMARY

Implementations of semiconductor devices may include: a microlens array formed of a plurality of microlenses. Each of the plurality of microlenses may have a first side and a second side. A layer of polymer may be formed over the second side of each of the plurality of microlenses and a low index box may be between adjacent microlenses of the plurality of microlenses.

Implementations of semiconductor devices may include one, all, or any of the following:

The polymer may be a fluoropolymer.

The layer of polymer may have a widest dimension of 250 nanometers.

The device may further include a filter array (CFA) in a box (CIAB) or a composite grid (CG) coupled with the first side of the microlens array.

The CIAB may include a material having a refractive index of 1.46.

The low index box may have a refractive index of 1.39.

The low index box may have a widest dimension of 150 nanometers.

The microlens array may be formed of a material having a refractive index of 1.6 to 1.8.

Implementations of semiconductor devices may include: a microlens array formed of a plurality of microlenses. Each of the plurality of microlenses may have a first side and a second side. The device may include a layer of polymer formed over the second side of each of the plurality of microlenses. The device may include one or more air gaps in a portion of the layer of polymer between adjacent microlenses of the plurality of microlenses.

Implementations of semiconductor devices may include one, all, or any of the following:

The one or more air gaps may be positioned in a low index box between each of the plurality of microlenses.

The polymer may be a fluoropolymer.

The one or more air gaps may have a longest dimension of 400 nanometers.

The device may further include a color filter array (CFA) in a box (CIAB) or a composite grid (CG) coupled to a first side of the micro lens array.

The CIAB may include a material having a refractive index of 1.46.

Implementation of semiconductors may be formed using an implementation of a method of forming semiconductors, the method may include: providing a semiconductor wafer. The semiconductor wafer may include a first side and a second side. The method may include forming a planar layer on the second side of the semiconductor wafer. The method may include forming a photoresist layer on the planar layer. The method may include forming a microlens array in the planar layer. The method may include coupling a polymer over and between each of a micro lens of the micro lens array.

Implementations of methods of semiconductor devices may include one, all, or any of the following:

Coupling a polymer over and between each of the microlenses may further include forming one or more air gaps in a portion of the layer of polymer surrounding each of the plurality of microlenses.

The one or more air gaps may have a longest dimension of 400 nanometers.

The polymer may include a low refractive index of 1.39.

The method may further include coupling a color filter array to the second side of the semiconductor wafer before forming the planar wafer.

The method may further include forming a box in a portion of the layer of polymer surrounding each of the plurality of microlenses, the box comprising a widest dimension of 150 nanometers.

The foregoing and other aspects, features, and advantages will be apparent to those artisans of ordinary skill in the art from the DESCRIPTION and DRAWINGS, and from the CLAIMS.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and:

FIG. 1 is a cross sectional view of an implementation of a microlens array;

FIG. 2 is a cross sectional view of an implementation of a semiconductor wafer with two pixels formed therein;

FIG. 3 is a cross sectional view of an implementation of a planar layer formed on an implementation of a semiconductor wafer;

FIG. 4 is a cross sectional view of a photoresist layer formed on an implementation of a planar layer;

FIG. 5 is a diagram of an implementation of a formation of a microlens array;

FIG. 6 is an implementation of a microlens array having air gaps in an implementation of a low refractive index polymer layer formed over the microlenses;

FIG. 7 is an implementation of a microlens array coupled with a composite grid (CG);

FIG. 8 is an implementation of a microlens array coupled with a color filter array (CFA) in a box (CIAB); and

FIG. 9 is an implementation of a microlens device having a low index box between adjacent microlenses.

DESCRIPTION

This disclosure, its aspects and implementations, are not limited to the specific components, assembly procedures or method elements disclosed herein. Many additional components, assembly procedures and/or method elements known in the art consistent with the intended microlens devices will become apparent for use with particular implementations from this disclosure. Accordingly, for example, although particular implementations are disclosed, such implementations and implementing components may comprise any shape, size, style, type, model, version, measurement, concentration, material, quantity, method element, step, and/or the like as is known in the art for such microlens devices, and implementing components and methods, consistent with the intended operation and methods.

Referring to FIG. 1, an implementation of a microlens device 2 is illustrated. The microlens device 2 includes a microlens array 4 formed of a plurality of microlenses 6. As illustrated in FIG. 1, the microlens array 4 is formed on a semiconductor wafer 8 having a first side 10 and a second side 12 and which contains pixels formed therein. The microlenses 6 are formed on a second side 12 of the semiconductor wafer 8 over a dielectric layer 14. In various implementations, the dielectric layer may be a high k dielectric layer. The dielectric layer may provide a ground connection and PAD to dissipate electrostatic charge.

As illustrated, each of the plurality of microlenses 6 have a first side 16 and a second side 18. For simplicity of representation, this cross sectional view only illustrates two microlenses 6 rather than the many microlenses typically formed in the array. In various implementations, a microlens array would include two or more microlenses to form a plurality of microlenses. The microlens array is formed of a translucent material such as, by non-limiting example, ultraviolet curable epoxy, spin on glass, light transmissive photoresist, phenol formaldehyde resins (PF), phenolic resins, or other materials suitable to allow light to pass through the lens. In various implementations, the microlenses may be formed of a material marketed under the tradename TOK which is a low refractive optical coating manufactured by TOKYO OHKA KOGYO CO., LTD. of Kawasaki, Japan. In various implementations, the microlens material may have a refractive index of 1.6 to 1.8. In some implementations, a refractive index of 1.6 may be used.

As illustrated in FIG. 1, a layer of polymer 20 is formed over the second side 18 of each of the plurality of microlenses 6. In various implementations, the polymer 20 may include a fluoropolymer. The polymer 20 as it is deposited, coats the second side 18 and at the intersection, at a certain point, no polymer is able to fill the space between adjacent microlenses as the layers of polymer 20 on each adjacent microlens approach each other. The effect of the inability of the polymer to fill the space at a certain point during the deposition is that an air gap 21 is created in the layer at this location between the adjacent microlenses. In various implementations, the air gaps 21 may have a longest dimension of about 400 nm, though larger or smaller longest dimensions may be used in various implementations. In some implementations, the fluoropolymer may be applied through, by non-limiting example, insitu deposition, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), sputtering, or any other method of applying a fluoropolymer.

In various implementations, the polymer may be any material (including, but not limited to a fluoropolymer) that has a refractive index around 1.395. Using materials having a lower refractive index may increase the quantum efficiency of a microlens device implementation. In various implementations, the layer of polymer may have a thickness 22 of about 250 nm. In still other implementations, the thickness 22 of the layer of polymer may be about 500 nm. In various implementations, as a result of the formation process, the one or more air gaps may be positioned in a low index box (low refractive index box) between each of the plurality of microlenses. The air gaps may further reduce reflection in the microarray lenses because air has a refractive index of 1.0 which is lower than the refractive index of the fluoropolymer which has a refractive index of approximately 1.3. In various other implementations, the refractive index of fluoropolymers may be reduced to 1.17.

Referring to FIGS. 2-6, an implementation of a microlens array at various steps in an implementation of a method of forming microarray devices (microlenses) is illustrated. The method may include providing a semiconductor wafer. Referring to FIG. 2, a semiconductor wafer 24 is illustrated. The semiconductor wafer includes a first side 26 and a second side 28. In various implementations, the semiconductor wafer may be a silicon or a silicon-containing wafer, though in various implementations, the wafer may be formed of, by non-limiting example, silicon-on-insulator, sapphire, ruby, gallium arsenide, glass, silicon dioxide, or any other semiconductor material type or desired substrate type. The method may include forming a dielectric layer 30 on the second side 28 of the semiconductor wafer 24. In various implementations, a grid structure may be used on the semiconductor wafer to provide physical ground protection. In some implementations, a pad may be used to dissipate electrostatic charge.

The method also includes forming a planar layer on the second side of the semiconductor wafer. Referring to FIG. 3, a planar layer 32 is illustrated formed on the second side 28 of the semiconductor wafer 24 over the dielectric layer 24. The planar layer may include optical coatings such as, by non-limiting example, oxides, rare earth metals, resins, ultraviolet curable epoxies, spin on glass, and other suitably optically transmissive materials. The planar layer may be formed using a coating process, such as, by non-limiting example, a spin coating process, a deposition coating process, a spray coating process or any other technique used to apply a planar layer of material. The method further includes forming a photoresist layer as a masking layer on the planar layer. Referring to FIG. 4, a masking layer 34 is illustrated after formation on the planar layer 32.

The method then includes forming a microlens array in the planar layer. The microlens array is formed as illustrated through etching 36 a plurality of microlenses 40 as illustrated in FIG. 5. The etching may include a two-step process. A double microlens may be formed through insitu transfer etching and by then low refractive index deposition. A dual etch microlens method may increase quantum efficiency (QE) in various implementations for improved device performance. The dual etch method may also reduce the optical cross-talk for modular transfer function (MTF) improvement, solve the channel difference (checker board effect) between adjacent microlenses, and/or create devices having higher fill-factor (F/F). Experimental data from a microlens array formed using the disclosed method and structure disclosed herein showed a 10% QE gain over microlens arrays formed using gapless and pin-cushion methods. The etching process described may also allow for controllability of various microlens properties such as, by non-limiting example, receiver operating characteristics (RoC), lens height, and/or F/F.

The method also includes coupling a low refractive index polymer over and between each microlens of the microlens array (see FIG. 6). In various implementations, the polymer may be a fluoropolymer. The polymer may be coupled to the microlens through insitu deposition as previously described, though any deposition method disclosed in this document may be utilized in various implementations. As previously described, the insitu deposition forms air gaps in a portion of the layer of polymer located between each of the plurality of microlenses. In an implementation of chemical vapor deposition (CVD) or PECVD used to couple the polymer to the microlens, non-conformal stack coverage creates a free path and no surface migration. Therefore, a narrow side of the trench eventually becomes blocked and the air-gap is formed below. In various implementations, the air gaps may have a longest dimension of about 400 nm or any longest dimension disclosed in this document. In some implementations, the polymer may have a refractive index of 1.39. In various implementations, a layer of polymer may have a thickness of about 250 nm or about 500 nm in various implementations. Referring to FIG. 6, the microlens array 42 is illustrated after coating of the microlenses 40 with a polymer 44. An enlarged view 46 of the space between adjacent microlenses is illustrated in FIG. 6 as well. As illustrated, an air-gap 48 is illustrated between adjacent microlenses. In various implementations, the air gap can be described as being within/located within a low refractive index box 50 formed between the microlenses. In various implementations, the box is formed by a spacing between individual microlenses and is filled with a low refractive index material such as, by non-limiting example, fluoropolymer, phenolic resins, and other suitable coating materials.

The methods described herein may provide a cost reduction due to simplification of the process. The method steps are reduced by using only one photoresist process (COAT/PHOTO/DEVELOP/BAKE) compared with gapless microlens processes. The method may be applicable to all products regardless of any pixel size in 200 mm and 300 mm products. Methods of forming microlenses with low refractive index boxes between adjacent microlenses may provide a total reflection effect from high angle incident light using efficient light collection into a photo-diode (pixel) below the microlens array that demonstrated a 4% QE gain in experimental data. Experimental data using a microlens array like those disclosed herein illustrated a 10% QE gain over pin-cushion devices. The microlens arrays formed by the methods described herein may provide a single focal point and narrow light shape capable of preventing QE losses. This method may also be simpler to combine with additional microlens process developments such as high index seed lenses, multi seed lenses, and colored lenses.

Referring again to FIG. 6, an implementation of a microarray (plurality of microlenses) formed by the described method implementation is illustrated. The microarray device 42 includes a microlens 40 coupled with a semiconductor wafer 24 having a first side and a second side. A first side of the microarray 40 is coupled to the second side of the semiconductor wafer. A dielectric layer 28 is formed between the semiconductor wafer 24 and the lenses 52 of the microarray 40. A fluoropolymer 44 is coupled to a second side of the plurality of lenses of the microarray. Air gaps 48 are illustrated in the fluoropolymer layer between adjacent lenses 52 of the microarray 40.

The microarray devices described herein and methods for forming the devices may be used with any pixel size. The method may also be used with standard filters such as, by non-limiting example, red green blue (RGB) filters, mono filters, color filter array (CFA) in a box (CIAB), composite grids (CG), or other devices capable of use in optical devices. In various implementations, the method may include coupling a color filter array (CFA) to the second side of the semiconductor wafer before forming the planar wafer.

An example of an implementation of a composite grid (CG) 54 coupled with a microarray 56 is illustrated in FIG. 7. An oxide layer 58 is located between each CG. Metal 60 is present in the oxide layer 58 between the CG 54. In various implementations, the metal may be tungsten (W). An implementation of a CIAB 62 coupled with a microarray 64 in a microarray device is illustrated in FIG. 8. As illustrated, an oxide material is coupled between each CIAB 62. In various implementations, the oxide 63 may have a refractive index around 1.46. In some implementations, the oxide layer may have a widest dimension of about 150 nm. A CIAB may be more efficient in increasing the Quantum Efficiency (QE) of implementation of a microarray device including a CG.

In various implementations, another implementation of a method of a forming a microarray device includes providing a semiconductor wafer with a first side and a second side. The method includes forming a planar layer on the second side of the semiconductor wafer. In various implementations, the planar layer may be formed of optical material such as low refractive index coating materials manufactured by TOKYO OHKA KOGYO CO., LTD. of Kawasaki, Japan or any other low refractive index coating material disclosed in this document. In some implementations, the refractive index of the planar layer may be 1.6. In other implementations, the refractive index of the planar layer, and resulting microlenses, may be between 1.6 and 1.8. The method may also include forming a photoresist layer on the planar layer and forming a plurality of microlenses using a transfer etching process like that disclosed herein to form a microlens array.

A gap may be formed between each of the plurality of microlenses through the etching process or through a separate patterning and etching process. In various implementations, the gap may have a widest dimension of about 150 nm. The method includes coupling a polymer over and between each of a microlens of the microlens array. In various implementations the polymer may include a fluoropolymer as previously described. In other implementations, the polymer may be an antireflective coating (ARC) such as phenol formaldehyde (PF) resin. The gap between the microlenses may be completely filled with the polymer. In various implementations, the polymer may have a refractive index of 1.395.

The method may also include coupling a color filter to a second side of the semiconductor die before forming the planar layer. In various implementations, the color filter may be a CIAB. The walls of the CIAB may be formed of silicon dioxide. The walls may have a widest dimension of about 150 nm and may have a refractive index of 1.46. The structure described may allow collimation of focused light in Si and may improve pixel QE, cross-talk, resolution (MTF) and global shutter efficiency by redirecting and collimating light from lower index filled about 150-200 nm gap walls of microlens gap and CIAB into a photodiode region from the storage node region of the global shutter pixel. Simulation results for a 2.74 μm back side illuminated (BSI) Global Shutter pixel with a color filter array like that that formed using the method implementation disclosed herein provided QE of 84.8% at 550 nm global shutter efficiency (GSE) which was 72.0 decibel (dB) over the 81% QE of a comparison gapless microlens array with no ARC between the microlenses. FIG. 9 illustrates an implementation of a microlens array and color filter made according to the previously described method.

Referring to FIG. 9, an implementation of a microlens device 66 having low index boxes 68 between adjacent microlenses 70 is illustrated. The device includes a microlens array 72 formed of a plurality of lenses 70. Each of the plurality of lenses 70 has a first side and a second side. A layer of ARC polymer 74 is formed over the second side of the each of the plurality of microlenses 70. The ARC polymer completely fills a gap 68 or low index box between adjacent microlenses 70. In various implementations, a widest dimension of the low index box is about 150 nm. As illustrated, in various implementations, a CIAB is coupled with a first side of each of the microlenses. In some implementations, each of the CIABs may have about 150 nm walls. As illustrated, the walls 76 of the CIABs may be formed of SiO₂ and may have a refractive index of 1.46. As previously described, the structure of this device may collimate focused light in Si to improve pixel QE, cross talk, resolution (MTF), and/or Global Shutter Efficiency by redirecting and collimating light from the lower index filled microlens gaps and CIAB into photodiode region from storage node region of global shutter pixel. A wide variety of microlens arrays and color filter combinations may be constructed using the principles disclosed herein.

In places where the description above refers to particular implementations of microlens devices and implementing components, sub-components, methods and sub-methods, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these implementations, implementing components, sub-components, methods and sub-methods may be applied to other microlens devices. 

What is claimed is:
 1. A semiconductor device comprising: a microlens array formed of a plurality of microlenses, each of the plurality of microlenses having a first side and a second side; a layer of polymer formed over the second side of each of the plurality of microlenses; and a low index box between adjacent microlenses of the plurality of microlenses.
 2. The semiconductor device of claim 1, wherein the polymer is a fluoropolymer.
 3. The semiconductor device of claim 1, wherein the layer of polymer has a widest dimension of 250 nanometers.
 4. The semiconductor device of claim 1, further comprising a filter array (CFA) in a box (CIAB) or a composite grid (CG) coupled with the first side of the microlens array.
 5. The semiconductor device of claim 4, wherein the CIAB comprises a material having a refractive index of 1.46.
 6. The semiconductor of claim 1, wherein the low index box has a refractive index of 1.39.
 7. The semiconductor of claim 1, wherein the low index box has a widest dimension of 150 nanometers.
 8. The semiconductor of claim 1, wherein the microlens array is formed of a material having a refractive index of 1.6 to 1.8.
 9. A semiconductor device comprising: a microlens array formed of a plurality of microlenses, each of the plurality of microlenses having a first side and a second side; a layer of polymer formed over the second side of each of the plurality of microlenses; and one or more air gaps in a portion of the layer of polymer between adjacent microlenses of the plurality of microlenses.
 10. The semiconductor device of claim 9, wherein the one or more air gaps are positioned in a low index box between each of the plurality of microlenses.
 11. The semiconductor device of claim 9, wherein the polymer is a fluoropolymer.
 12. The semiconductor device of claim 9, wherein the one or more air gaps have a longest dimension of 400 nanometers.
 13. The semiconductor device of claim 9, further comprising one of a color filter array (CFA) in a box (CIAB) or a composite grid (CG) coupled to a first side of the microlens array.
 14. The semiconductor device of claim 9, the CIAB comprises a material having a refractive index of 1.46.
 15. A method of forming a semiconductor device, the method comprising: providing a semiconductor wafer, the semiconductor wafer comprising a first side and a second side; forming a planar layer on the second side of the semiconductor wafer; forming a photoresist layer on the planar layer; forming a microlens array in the planar layer; and coupling a polymer over and between each of a microlens of the microlens array.
 16. The method of claim 15, wherein coupling a polymer over and between each of the microlenses further comprises forming one or more air gaps in a portion of the layer of polymer surrounding each of the plurality of microlenses.
 17. The method of claim 16, wherein the one or more air gaps have a longest dimension of 400 nanometers.
 18. The method of claim 15, wherein the polymer comprises a low refractive index of 1.39.
 19. The method of claim 15, further comprising coupling a color filter array to the second side of the semiconductor wafer before forming the planar wafer.
 20. The method of claim 15, further comprising forming a box in a portion of the layer of polymer surrounding each of the plurality of microlenses, the box comprising a widest dimension of 150 nanometers. 